The following U.S. patent applications filed concurrently herewith: Ser. No. 09/659,876, entitled xe2x80x9cMethod and Apparatus for Regulating a Voltagexe2x80x9d by Timothy J. Dupuis et al; Ser. No. 09/659,636, entitled xe2x80x9cDual Oxide Gate Device and Method for Providing the Samexe2x80x9d by Timothy J. Dupuis et al; Ser. No. 09/659,874, entitled xe2x80x9cRF Power Amplifier Device and Method for Packaging the Samexe2x80x9d by Timothy J. Dupuis et al; Ser. No. 09/660,123, entitled xe2x80x9cPower Amplifier Circuitry and Methodxe2x80x9d by Susanne A. Paul et al; and Ser. No. 09/659,873, entitled xe2x80x9cApparatus and Method for Providing Differential-to-Single Ended Output Conversion and Impedance Transformationxe2x80x9d by Susanne A. Paul et al, are expressly incorporated herein by reference.
This invention relates to the field of power amplifiers. More particularly, this invention relates to radio frequency (RF) power amplifiers for use with wireless transmission systems.
This invention is useful in, for example, cellular telephone systems, and other wireless transmission systems.
Some prior art RF power amplifiers use two active switching devices to generate a square wave signal. An output load network filters and transforms the signal into a sinusoidal output signal which is then transmitted. There are various problems associated with this type of power amplifiers Perhaps the largest problem with power amplifiers involves the efficiency of the amplifiers. When RF power amplifiers are used to produce high power signals, such as with transmitters, it is desired to have efficient amplifiers in order to conserve power and adequately dissipate heat. This problem is especially hard to overcome in designs utilizing CMOS devices.
Another problem relates to the use of an isolation transformer. Some prior art RF power amplifiers include a transformer connected between the pre-driver circuitry and the amplifier circuit. This presents various issues. First, a transformer is required, which uses valuable real estate on a printed circuit board (PCB) and also increases the cost of the amplifier. In addition, the transformer consumes power and generates heat.
Another problem with prior art power amplifiers involves voltage regulators. During battery charge up, the battery voltage can be much higher than the steady-state voltage. Applying this high voltage directly to a CMOS power amplifier can cause breakdown problems. Therefore, a voltage regulator may be required to provide a regulated voltage source. However, when the battery charge is high and the power amplifier is transmitting at maximum power, there is a high power dissipation in the voltage regulator which could exceed the package power rating of an integrated circuit.
When selecting the types of devices to be used in a CMOS design, such as an RF power amplifier, certain tradeoffs exist. For example, devices with smaller gate oxide thickness are faster and take up less space. However, as the gate oxide thickness gets smaller, the breakdown voltage of the device also gets smaller. Therefore, when selecting devices in a CMOS design a problem develops in getting a suitable breakdown voltage as well as a suitable speed for a device.
Another problem with prior art power amplifiers relates to amplifiers using a push-pull architecture. A push-pull architecture requires very low inductance and resistance in the ground and signal connections of the integrated circuit to the PCB. In a typical wire bond package, the bond wire inductance can be large enough to cause problems. In addition, the resistance of on-chip wiring using thin on-chip conductors can cause significant losses.
An apparatus of the invention is provided for an RF power amplifier including an input stage and a push-pull amplifier coupled to the input stage having first and second transistors, wherein the first and second transistors are driven by tuned circuits.
Another embodiment of an RF power amplifier includes first and second switching devices coupled in series between a voltage source and ground for providing an amplified signal to a load and a third switching device having an input coupled to an RF input signal and having an output connected to a gate of one of the first or second switching devices.
Another embodiment of the invention provides a driver circuit for driving a push-pull type RF amplifier having first and second switching devices and an input node formed by the gate of one of the switching devices, the driver circuit including a switching device having an input connected to an RF input signal and an output connected to the input node and tuned circuitry connected to the RF amplifier for tuning the RF amplifier to a desired frequency.
Another embodiment of the invention provides a method of driving a push-pull type amplifier operating at a desired frequency including the steps of providing a push-pull type amplifier having first and second switching devices connected in series between a voltage source and ground, coupling a driving circuit to the amplifier, and providing tuning circuitry for tuning the amplifier to the desired frequency.
Other objects, features, and advantages of the present invention will be apparent from the accompanying drawings and from the detailed description that follows below.